In certain types of distributed estimation, a large number of inexpensive sensors are scattered, measuring a desired quantity, θ, and transmitting the measurement back to a fusion center (FC), where these measurements are fused into a single estimate, {circumflex over (θ)}. An example of such a scenario is surveillance in an inaccessible area: sensors are airdropped into a region and there is a fusion center in the area. The sensors measure some physical quantity in the presence of noise. In this or other mobile low-power sensor network applications, power efficiency is a key design attribute influencing usability of the system.
There are a variety of ways to transmit the data from each sensor to the fusion center. Each individual sensor can transmit its data to the fusion center using an orthogonal signaling scheme, which makes each sensor's measurement independently discernible, but also requires a total system bandwidth that grows with the total number of sensors. This increasing bandwidth requirement limits the attainable sensor sampling rate. This may be acceptable if the number of sensors is small, but may not be applicable when the number of sensors is large. A different technique is to use an estimation algorithm which does not need to attain the values of individual sensor measurements orthogonally, but instead operates on an aggregate received value. One estimation algorithm that can operate using a shared bandwidth is Amplify-and-forward (AF).
An assumption made in AF systems is that the transmitter is either inherently linear or has been linearized by a predistorter. Though linearity is desirable for producing accurate estimates, it significantly reduces the power efficiency of the transmitting sensors. Many papers have been published on boosting the energy-efficiency of wireless sensor networks at the system-level by optimally allocating transmitted output power among the sensors, but none examines the battery power required to generate the output.
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The terms “couple,” “coupled,” “couples,” “coupling,” and the like should be broadly understood and refer to connecting two or more elements or signals, electrically, mechanically or otherwise. Two or more electrical elements may be electrically coupled, but not mechanically or otherwise coupled; two or more mechanical elements may be mechanically coupled, but not electrically or otherwise coupled; two or more electrical elements may be mechanically coupled, but not electrically or otherwise coupled. Coupling (whether mechanical, electrical, or otherwise) may be for any length of time, e.g., permanent or semi permanent or only for an instant.
“Electrical coupling” and the like should be broadly understood and include coupling involving any electrical signal, whether a power signal, a data signal, and/or other types or combinations of electrical signals. “Mechanical coupling” and the like should be broadly understood and include mechanical coupling of all types. The absence of the word “removably,” “removable,” and the like near the word “coupled,” and the like does not mean that the coupling, etc. in question is or is not removable.